Battery charging problem

If you can provide more information you will get better answers. How old are the batteries? What type 12v marine, 6v golf cart,etc? When you stored the MH were they fully charged(at least 12.6 resting voltage)? How many amps does your converter charge at? When you say dead what was the resting voltage?

How did they test the batteries if they are dead???? Like others have said, dead battery usually equals bad battery. If you have had freezing temps and they were dead, they have been frozen and they are junk!! Do not try to charge a battery that is or has been frozen, they can and will explode!!!

I trashed my first battery on a new trailer. Thought I was taking care of it, but I left the battery hooked uo and the parasitic draw basically ruined it. This happen over the summer on out property in the mountains. This last summer I disconnect the battery when not at the property.

Agree with earlier comment. Lead acid batteries do not appreciate complete discharge. When bad they will not recover.

When leaving it sitting for weeks or months it is a good idea to throw the battery disconnect switch if you have one, or lift one of the battery cables if you don't.

If you are still there you can get an inexpensive analog multimeter for about $10 or a digital multimeter for about $20 at Walmart that will be good for those kind of measurements. And just leave it in the camper.

Flat dead is bad for any lead-acid battery. You have lost capacity to sulfation and probably need an equalization charge as a minimum.
Unknown converter model is hard to comment on.
Not knowing what voltage is getting to the battery makes it hard to know if you have an open circuit or dead converter. Although with lights on the converter seems to be working.
Do you have a battery switch that was off?
Most converters will take 24 to 48 hours to charge a low battery.

We have one but forgot to bring it this trip. Will try it next trip. Thanks for the help.

Completely discharging a battery and leaving it that way is probably the worst thing you can do to one. The batteries are likely no good anymore.
Some older converters would only put out 10 amps or so to charge batteries. If you have 2 group 27 batteries that are fully depleted that's about 200 amp/hours. If your charger only puts out 10 amps it would take over 20 hours of generator running to recharge them.
The only way to know what's happening is with a volt meter; do you have one? If so, check the voltage at the battery terminals with the generator off and then with it running. It should be higher with it running, hopefully around 13 or 14 volts.

How long is "a while"? With some converters, it can take a very long time to charge the batteries.

If the batteries were truly run down all the way to dead, that could very well have destroyed them, unfortunately.